The present invention broadly relates to marine propulsion systems and, more particularly, to a reduction and reversing gear for propulsion systems which makes it possible to obtain a large variety of reduction ratio ranging between about 2.0 and 8.0 by making use of a clutch case for small reduction ratio of conventional reduction gear.
Hitherto, various measures have been taken to obtain a large variety of the reduction ratio, the typical examples of which are: (a) to use the clutch case for the large reduction ratio also as the clutch case for the small reduction ratio and (b) to use different clutch cases for various reduction ratios, the clutch cases having different distances between the input and the output shafts.
The first measure (a), however, poses various problems such as raised cost and increased weight, although this measure eliminates the necessity of different clutch cases. In addition, this measure makes it difficult to install the reduction and reversing gear on the hull. Namely, since the clutch case has a large vertical dimension, the lower part inconveniently abuts the bottom of the hull, if the reduction and reversing gear is installed at the stern of the hull. To avoid this, it is necessary to shift the position of the clutch case toward the bow of the hull. Apparently, this requires a large volume of the engine room.
In the method (b) above, the mounting of the engine, as well as the reduction and reversing gear on the hull, is made difficult because the different clutch cases provide different distances between the input and the output shafts. Namely, considerable work is required to modify the hull and the engine bed or the bed for the reduction and reversing gear, to meet the various distances between the input and output shafts of the reduction and reversing gear.
Generally, the reduction and reversing gear for marine propulsion systems has an input shaft disposed at an upper portion of the clutch case and an output shaft disposed at a lower portion of the clutch case in parallel with the input shaft. The input shaft carries a multiple disc clutch, while the output shaft carries a large gear. The large gear engages a small gear which in turn is adapted to be connected to the input shaft through the medium of the clutch.
It is to be noted that this construction of the reduction and reversing gear provides a comparatively large vacant space beneath the clutch and around the output shaft.
Upon recognition of this point, the present invention proposes to make an efficient use of this vacant space, by mounting in this space a planetary gear type reduction gear so that an additional reduction may be achieved between the large gear and the output shaft.
More specifically, according to the invention, there is provided a reduction and reversing gear for marine propulsion systems the reduction and reversing gear having: a clutch case; an input shaft mounted on an upper portion of the clutch case; an output shaft mounted at a lower portion of the clutch case and extending in parallel with the input shaft; an ahead unit including a multiple disc clutch mounted on the input shaft and having a clutch housing adapted to rotate unitarily with the input shaft and a small gear mounted on the input shaft and adjacent to the multiple disc clutch, the small gear being adapted to be connected to and disconnected from the input shaft in accordance with the state of the multiple disc clutch; a large gear mounted on said output shaft for engagement with said small gear; and an astern unit disposed in parallel with said ahead unit and including a multiple disc clutch having a clutch housing operatively connected to the clutch housing of the ahead unit and a small gear for engagement with said large gear; wherein the improvement comprises a planetary gear type reduction gear disposed in the space below the multiple disc clutch of said ahead unit, the planetary gear type reduction gear being connected at its one side to the large gear and to the output shaft at its other side.
Other features and advantages of the invention will become clear from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.